1. Field of the Invention
The invention relates to a method for manufacturing a helmet, in particular for a pilot, wherein the helmet carries optics which must be precisely aligned with the pilot's eyes and must remain aligned when the helmet is subject to large forces. The invention also relates to an apparatus for determining the precise positioning of a subject's pupils with respect to a 3-D model of the subject's head.
2. Description of the Related Art
Optical display systems have added substantial mass to and adversely affected the center of gravity (CG) of typical flight helmets. At the same time, positioning and alignment of the optical system with respect to the user's eyes is very critical; the usable region of eye locus around the design position may be less than a 5 mm radius hemisphere.
The accurate eye-positioning requirement has generally been addressed by means of adjustable helmet fitting/suspension systems and/or adjustable optics. In either case, the added mass and adverse CG effects due to the optics leads to very large forces tending to shift the helmet location on the head during high-G aircraft maneuvers; the shift at +9 Gz is commonly great enough to cause total visual loss of the optical display.
It is accordingly very important not only that the helmet be precisely fitted to the pilot's head, but also that the optics be precisely fitted to the helmet so that it is precisely aligned with the pilots eyes and remains aligned when subjected to large forces.
Adjustable fitting/suspension systems may serve well as static eye positioning mechanisms. However, due to comfort-induced pressure limitations and the inability to eliminate vertical slack in the system (because of the relatively low weight of the helmet and optics at +1 Gz as compared to +9 Gz), vertical helmet motion due to the suspension tightening under the force of the 9-times increase in the helmet's weight at +9 Gz cannot be prevented.
U.S. Pat. No. 5,584,073 discloses a helmet system wherein the position of the helmet with respect to the wearer's head is adjusted to position the eyes where required. However system elasticity and concentrated pressure points contribute to helmet motion and therefore to difficulty in maintaining the position of the optics relative to the eyes under high loads.
U.S. Pat. No. 6,279,172 discloses a helmet system which reduces the aforementioned elasticity by using rigid plastic straps instead of nylon webbing, and reduces pressure in the brow region by using a poured foam forehead pad. However the performance was still less than ideal.
U.S. Pat. No. 6,487,786 discloses a method and a tool for aligning a helmet with respect to a wearer's head in the above described systems, but does not solve the problem of relative motion between the helmet and the wearer's head under high G forces.
Adjustable optics may assist in initial static fitting of the system to the wearer's eye locus, perhaps simplifying the fitting/suspension system. However, it cannot compensate for helmet movement under G-forces. Also, many current optical systems are not adjustable, for reasons of availablespace, complexity, mass, and tolerances inherent in adjustment systems.
U.S. Pat. No. 5,866,826 discloses a method which involves fitting the helmet to the pilot's head, determining the position of the subject's eyes with respect to the helmet by using an optical stand, and then fitting the optics to the helmet in accordance with the determined position using a jig to position the helmet so that the optics can be mounted using shims and the like. This results in a helmet which is virtually dedicated to a particular pilot, since both the lining and the optics are custom fitted.